diff --git a/tools/doc/html.js b/tools/doc/html.js
index c631afe534e103..9089ce7e443232 100644
--- a/tools/doc/html.js
+++ b/tools/doc/html.js
@@ -73,10 +73,8 @@ function processContent(content) {
   if (content.includes('<h6>')) {
     throw new Error('Cannot increment a level 6 header');
   }
-  if (/<h[1-5][^>]/.test(content) {
-    throw new Error('Cannot parse header tag with attributes');
-  }
-  content.replace(/(?<=<\/?h)[1-5](?=>)/g, (level) => level + 1);
+  // `++level` to convert the string to a number and increment it.
+  content = content.replace(/(?<=<\/?h)[1-5](?=[^<>]*>)/g, (level) => ++level);
   // Wrap h3 tags in section tags.
   let firstTime = true;
   return content